5.3. Cassandra Connector

5.3. Cassandra Connector

The Cassandra connector allows querying data stored in Cassandra.

Compatibility

Connector is compatible with all Cassandra versions starting from 2.1.5.

Configuration

To configure the Cassandra connector, create a catalog properties file
etc/catalog/cassandra.properties with the following contents,
replacing host1,host2 with a comma-separated list of the Cassandra
nodes used to discovery the cluster topology:

connector.name=cassandra
cassandra.contact-points=host1,host2

You will also need to set cassandra.native-protocol-port if your
Cassandra nodes are not using the default port (9042).

Multiple Cassandra Clusters

You can have as many catalogs as you need, so if you have additional
Cassandra clusters, simply add another properties file to etc/catalog
with a different name (making sure it ends in .properties). For
example, if you name the property file sales.properties, Presto
will create a catalog named sales using the configured connector.

Configuration Properties

The following configuration properties are available:

Property Name

Description

cassandra.contact-points

Comma-separated list of hosts in a Cassandra cluster. The Cassandra
driver will use these contact points to discover cluster topology.
At least one Cassandra host is required.

Consistency levels in Cassandra refer to the level of consistency
to be used for both read and write operations. More information
about consistency levels can be found in the
Cassandra consistency documentation. This property defaults to
a consistency level of ONE. Possible values include ALL,
EACH_QUORUM, QUORUM, LOCAL_QUORUM, ONE, TWO,
THREE, LOCAL_ONE, ANY, SERIAL, LOCAL_SERIAL.

cassandra.allow-drop-table

Set to true to allow dropping Cassandra tables from Presto
via DROP TABLE (defaults to false).

cassandra.username

Username used for authentication to the Cassandra cluster.
This is a global setting used for all connections, regardless
of the user who is connected to Presto.

cassandra.password

Password used for authentication to the Cassandra cluster.
This is a global setting used for all connections, regardless
of the user who is connected to Presto.

Note

If authorization is enabled, cassandra.username must have enough permissions to perform SELECT queries on
the system.size_estimates table.

The following advanced configuration properties are available:

Property Name

Description

cassandra.fetch-size

Number of rows fetched at a time in a Cassandra query.

cassandra.partition-size-for-batch-select

Number of partitions batched together into a single select for a
single partion key column table.

cassandra.split-size

Number of keys per split when querying Cassandra.

cassandra.client.read-timeout

Maximum time the Cassandra driver will wait for an
answer to a query from one Cassandra node. Note that the underlying
Cassandra driver may retry a query against more than one node in
the event of a read timeout. Increasing this may help with queries
that use an index.

cassandra.client.connect-timeout

Maximum time the Cassandra driver will wait to establish
a connection to a Cassandra node. Increasing this may help with
heavily loaded Cassandra clusters.

cassandra.client.so-linger

Number of seconds to linger on close if unsent data is queued.
If set to zero, the socket will be closed immediately.
When this option is non-zero, a socket will linger that many
seconds for an acknowledgement that all data was written to a
peer. This option can be used to avoid consuming sockets on a
Cassandra server by immediately closing connections when they
are no longer needed.

cassandra.retry-policy

Policy used to retry failed requests to Cassandra. This property
defaults to DEFAULT. Using BACKOFF may help when
queries fail with “not enough replicas”. The other possible
values are DOWNGRADING_CONSISTENCY and FALLTHROUGH.

cassandra.load-policy.use-dc-aware

Set to true to use DCAwareRoundRobinPolicy
(defaults to false).

cassandra.load-policy.dc-aware.local-dc

The name of the local datacenter for DCAwareRoundRobinPolicy.

cassandra.load-policy.dc-aware.used-hosts-per-remote-dc

Uses the provided number of host per remote datacenter
as failover for the local hosts for DCAwareRoundRobinPolicy.

cassandra.load-policy.dc-aware.allow-remote-dc-for-local

Set to true to allow to use hosts of
remote datacenter for local consistency level.

cassandra.load-policy.use-token-aware

Set to true to use TokenAwarePolicy (defaults to false).

cassandra.load-policy.shuffle-replicas

Set to true to use TokenAwarePolicy with shuffling of replicas
(defaults to false).

cassandra.load-policy.use-white-list

Set to true to use WhiteListPolicy (defaults to false).

cassandra.load-policy.white-list.addresses

Comma-separated list of hosts for WhiteListPolicy.

cassandra.no-host-available-retry-timeout

Retry timeout for NoHostAvailableException (defaults to 1m).

cassandra.speculative-execution.limit

The number of speculative executions (defaults to 1).

cassandra.speculative-execution.delay

The delay between each speculative execution (defaults to 500ms).

Querying Cassandra Tables

The users table is an example Cassandra table from the Cassandra
Getting Started guide. It can be created along with the mykeyspace
keyspace using Cassandra’s cqlsh (CQL interactive terminal):

Limitations

Queries without filters containing the partition key result in fetching all partitions.
This causes a full scan of the entire data set, therefore it’s much slower compared to a similar
query with a partition key as a filter.

IN list filters are only allowed on index (that is, partition key or clustering key) columns.

Range (< or > and BETWEEN) filters can be applied only to the partition keys.